This invention relates to electrical test and measurement systems and, more particularly, to systems for testing and measuring the performance of space satellite antennas or other highly complex antennas in a far field environment.
The performance of the antennas aboard a space communications satellite is crucial to the success of the mission of that satellite. Accordingly, it is important to make extensive ground based tests and measurements on these antennas to ensure successful operation.
A typical satellite microwave antenna test program includes the measurement of antenna gain as a function of several variables. These variables may include antenna orientation in both azimuth and elevation, signal frequency, antenna pattern and signal polarization. An antenna may have more than one port through which signals are fed; and in some cases, it may be necessary to make the gain measurements using different ports. Consequently, the number of gain measurements to be made is often quite high. The physical acts and time necessary to accomplish such measurements have in the past been a major item of expense in the construction and testing of satellite communications systems.
In one particular system, for example, it is necessary that the antenna system be tested for gain using several different antenna configurations with up to six ports each with twenty individual frequencies at approximately seventy different elevation angles and seventy different azimuth angles. In addition, it is necessary to test the antenna for three different signal polarizations. In all, a total of approximately ten million individual gain measurements need be made.
The prior art method of making such measurements utilized phase locking receivers which, at best, could be moved very slowly through a limited number of frequencies due to the need to search for, locate, and lock on to each new frequency. The prior art systems often lose lock on a frequency during operation and cause the test in progress to be aborted. Moreover, prior art systems switch relatively slowly between no more than two ports. Finally, prior art systems require individual computer commands to switch, measure, store data, and to read the antenna position, a time consuming process.
It is therefore an object of the present invention to reduce the time and cost required for testing and measuring the performance of space satellite antennas.